Radial arm saws of the type described in the present invention generally include a track guiding a saw arm with a blade attached thereto. The blade rotates in clockwise fashion propelling the saw along the track towards the user. The saw is moved towards the user with one hand while the wood being cut is held in a fixed position with the other hand. A common hazard experienced with the radial saw is inadvertent acceleration of the saw in the direction of the user. This is due to the clockwise rotation of the blade as the saw is moved through the wood. The wood is held against a barrier referred to as fence which prevents the saw from shooting the wood off a support away from the user. Thusly, the wood being cut presents a fixed base against which the saw rotates. The rotation of the saw blade is continually forcing the saw along the saw track towards the user.
Various types of radial arm saw guards have been developed. U.S. Pat. No. 2,522,789 to Johnson, issued Sept. 19, 1950 discloses a radial arm mounting for power driven saws providing no guard. U.S. Pat. No. 3,884,101 to Silkin, issued May 20, 1975 discloses a radial arm saw guard for the exposed lower portion of the blade of the saw. U.S. Pat. No. 4,043,237 to Pyle, issued Aug. 23, 1977 discloses a transparent awareness guard in the form of a flat plate form attached to a conventional upper saw guard of a radial arm saw. U.S. Pat. No. 4,176,571 to Batson, issued Dec. 4, 1979 discloses a guard mechanism for a radial saw comprising a guard pivotally mounted to a housing for covering a front portion of the blade. U.S. Pat. No. 4,637,288 to Olsen et al, issued Jan. 20, 1987 discloses a saw apparatus including a safety device comprising means for gripping, positioning and clamping a workpiece relative to a workpiece support structure and a second normally biased off switch connected in series with a first normally biased off switch requiring both hands of an operator to be holding onto normally off switches to actuate the saw mechanism. None of the aforementioned patents provides any means for breaking the movement of a radial arm saw if the saw moves towards the user at a speed greater than a predetermined safe speed.
Various patents have issued with regard to safety brakes for saws. For example, U.S. Pat. No. 2,434,174 to Morgan, issued Jan. 6, 1948 discloses a safety brake for a bandsaw blade. The brake automatically stops and firmly holds the blade in the event that it should break or become too loose. The U.S. Pat. No. 2,500,321 to Petersen, issued Mar. 14, 1950 discloses an automatic hydraulic brake for bandsaws for instantly stopping relative motion between the tool and the work support of the machine tool upon stopping of the drive motor or breakage of the tool. Neither of these patents relate to the problems encountered in radial arm saws nor the specific problem of a radial arm saw inadvertently accelerating in the direction of the user.
U.S. Pat. No. 2,984,268 to Vuichard, issued May 16, 1961 discloses a manually actuated saw brake in combination with a radial arm saw. The brake specifically operates to quickly halt the rotation of the cutting element after deenergization of the cutting element motor. The patent does not relate to inadvertent acceleration of the saw in the direction of the user.
Other patents relate to anti-kickback devices. An example of this type of disclosure is the U.S. Pat. No. 4,212,214 to Bippus, issued Jul. 15, 1980. The Bippus patent discloses an anti-kickback device for mounting on table saws or radial arm saws that prevents the saw from throwing the board being cut back into the operator doing the feeding.
Although the aforementioned patents relate to safety devices and many relate to safety guards for radial arm saws, none of the aforementioned patents recognize the problem of inadvertent acceleration of the saw in the direction of the user and accordingly, none of the aforementioned patents disclose or even suggest a solution to the problem.